RSS service provider Feedburner's informal study on RSS Aggregator market statistics is providing an early benchmark for measuring the nascent sector.

But Feedburner said don't overlook its caveats; another blogging executive cautioned that the stats only count one type of aggregator.

Feedburner, an RSS/Atom service for publishers that provides
statistics as well as affiliate links for feeds, said aggregator Bloglines has the most market share among RSS feed aggregators.

Its numbers are based on an aggregate circulation of the top 800 feeds that it managed as of January 6, 2005. According to the company, there were
719 different RSS clients that polled their top 800 feeds, which is a
dramatic growth of almost 76 percent since September when it recorded
only 409 different clients.

Bloglines took the top spot in the measure of FeedBurner's feeds with a
32.86 share, almost double the share of the next closest client, NetNewsWire with 16.95 percent of the feeds.

Mozilla Firefox's Live Bookmarks
feature was third at 7.78 percent, Pluck fourth with 7.2 percent and
Newsgator at 4.45 percent rounded out the top five.

But the results also noted plenty of caveats, which underscores the fundamental difficulty in measuring the market so far.

For example, non-reporting proxies (unlike Bloglines or MyYahoo) don't report the number of unique RSS subscribers on whose behalf they are making http requests. Such a measure could skew the number since those proxies may have large numbers of users.

Web-based aggregators like MyYahoo may also skew the statistics
since they count all subscribers to a feed each day, regardless of
whether the subscribers actually read or checked the feed.

Bloglines, another Web-based aggregator, may also have an unfair advantage as well, since Feedburner's feeds
are mostly from blogs, which is Bloglines' specialty. Traditional media feeds from publishers (such as internetnews.com for
example) may very well show a different picture.

"Simply removing our top 10 feeds from this data results in a wildly
different market share list, possibly because of clients that ship with
one or more of our top 10 feeds as a default," Feedburner said in its own blog post about the results.

All of this points to the caution not to read too much into this single
data point, it continued. "We could make qualifications about everything on the list.
Your mileage may vary, caveat emptor, mea culpa, c'est la vie."

Mark Fletcher, founder and CEO of Bloglines, said any study of the RSS feed market needs to accurately measure subscriber levels. "And that's
easier said than done," he told internetnews.com. "The big
issue is accounting for the distinct differences in the way Web services
and desktop newsreaders behave."

Fletcher explained that a Web service like Bloglines pings RSS feed
servers at regular predictable intervals, whereas desktop aggregators
may
hit sites over and over again for the same user. In his opinion, this
means that the desktop user base is probably being over-counted.

"Beyond that, there's a red herring created by default subscriptions
(built into desktop software) that can skew results in ways that don't
reflect the real user base," Fletcher said. "These are key challenges that
a serious study will have to address to come up with credible numbers for
this market."

Blogger Richard MacManus, whose December post about his own RSS client stats was noted by Feedburner, also observed that his top three clients were the same as those in Feedburner's stats.

"However, the gap that Bloglines has is nowhere near as large as it was in my stats and NetNewsWire is a very healthy second (still only just over
half of Blogline's share however!)," MacManus wrote. "This augers well for
competition in the RSS Aggregator space, because it's always a worry when
one company monopolizes the competition."

In the meantime, Bloglines certainly isn't complaining about its rank in the FeedBurner stats. "It's great that people are trying
to get their arms around how big the RSS user base is and better
understand what this market looks like," said Bloglines spokesperson Cathy Thompson. "And of course we love it whenever
Bloglines is called out as number one."